Acacia nilotica ssp. indica L.

Title: Acacia nilotica ssp. indica L.

Scientific Name: Acacia nilotica ssp. indica L.

Common Name: prickly acacia, gum arabic tree

Source & more images (via ALA)

Habitat: Prefer tropical and subtropical climates. Found in woody grasslands and savannas. In northern Australia, found in Mitchell grasslands. Occurs on a wide range of soil types (DNRE 2004).

Distribution:

Original source via CABI

Invasiveness Assessment

ESTABLISHMENT

1. Germination requirements? ‘Seeds germinate after significant rainfall in late spring and summer’ (DNRME 2004) ‘…germination does not occur until triggered by water penetrating the hard seed coat. Germination occurs between 14° and 37°C. (Mackey 1998). Requires natural seasonal disturbance of rainfall and summer temperatures

2. Establishment requirements? ‘..but seedlings are shade intolerant. Although seedling establishment can occur in drier times, survival is low. If rainfall following germination is below average, the majority of seedlings on black soil will die within two years’ (Mackey 1998). Seedlings require open conditions and regular rainfall. …

3. How much disturbance is required? Dense infestations occur where there is a plentiful supply of water, for example, along watercourses and bore water drains. With an abundant supply of water and little shading by other plants, growth is rapid, but, ‘…on open downs where it is drier, a good grass cover may reduce growth’ (Mackey 1998). More likely to establish in disturbed situation where there is little competition.

GROWTH / COMPETITIVE

4. Life form? Tree, commonly to 6 metres, but can grow to 15 metres in optimal situation (Mackey 1998). Other life form.

5. Allelopathic properties? None described. Growth of perennial grasses under the canopy is greatly inhibited particularly during dry periods, however, annual and ephemeral species appear to be unaffected. Effect due to competition perennials for moisture and nutrients ( Mackey 1998)

6. Tolerates herb pressure? Seedlings are spiny, but sheep are known to browse on the lower branches of established plants. Domesticated animals consume the abundant seedpods in preference to the tree (Mackey 1998). Tolerates herbivory pressure.

7. Normal growth rate? Given access to water, seedling growth is rapid (Mackey 1998).

8. Stress tolerance to frost, drought, w/logg, sal. etc? It is reported that frost kills young plants and prevents seed set in older, established trees (Mackey 1998). However, in some frost prone areas in Queensland infestations of prickly acacia are established and spreading. Prickly acacia tolerates salinity if fresh water is present. It has a deep taproot, which enables it to survive dry periods. In Africa it is known to tolerate seasonal waterlogging (Duke 1983). Tolerates two or more stressors.

REPRODUCTION

9. Reproductive system? Reproduces sexually; self and cross pollination. Most flowers are functionally male while others are hermaphroditic (Mackey 1998). Prickly acacia does not reproduce vegetatively.

10. Number of propagules produced? Annually each tree produces an average of about 30000 seeds (Mackey 1998).

11. Propagule longevity? In bore drains (i.e. where water is plentiful) seed half-life was found to be 10 months, but some seed is known to survive up to seven years (Mackey 1998).

12. Reproductive period? Prickly acacia is known to live for up to 60 years (DNRME 2004).

13. Time to reproductive maturity? The plant reaches sexual maturity between 2 to 5 years (DNRME 2004).

DISPERSAL

14. Number of mechanisms? Domestic animals, particular cattle are the most important vectors of seed. Ingested seed can remain in cattle for up to six days leading to viable seed being dispersed over large distances. Other vectors are floodwaters and wind (<25m) (Mackey 1998).

15. How far do they disperse? Depending upon cattle movement, dispersal would be at least one kilometre, possibly greater (Mackey 1998).

Impact Assessment

RECREATION

1. Restrict human access? Shrub or small tree from 7 to 9 m high. ‘Because of its rapid growth in favourable seasons and the presence of long spines or prickles, dense thickets of prickly acacia, impenetrable to stock, develop. Thickets along thousands of kilometres of bore drains prevent access to water’ (Parsons & Cuthbertson 2001). Major impediment to access waterways.

2. Reduce tourism? Because of infestation by prickly acacia, “…the Mitchell grass downs are being converted into a thorny scrubland similar to the African thornveld” (Mackey 1998). Weeds presence is obvious to visitors.

3. Injurious to people? Young stems are armed with stout stipular spines 5 to 50 mm long, Spines may be absent on older stems. Dogs cannot be used for mustering purposes because of spines on the ground (Parsons & Cuthbertson 2001). Potential for injury throughout the year.

4. Damage to cultural sites? Shrub or small tree from 7 to 9 m high (Parsons & Cuthbertson 2001). Moderate visual effect.

ABIOTIC

5. Impact flow? Terrestrial species (Parsons & Cuthbertson 2001).

6. Impact water quality? Terrestrial species (Parsons & Cuthbertson 2001).

7. Increase soil erosion? “…a moderate canopy cover of prickly acacia reduces grass cover markedly and changes the relative abundance of native plant species in favour of forbs and annual grasses” (Mackey 1998). “Exacerbates and accelerates soil erosion” (ARMCANZ 2001).

8. Reduce biomass? “In Australia, it occurs as a weed, principally along streams and bore drains, in the semi-arid tussock and hummock grasslands” (Parsons & Cuthbertson 2001). Biomass would increase in these situations.

9. Change fire regime? “…prickly acacia does not seem susceptible to fire” (Mackey 1998). Suppression of grass species also reduces fire risk. Minor change to frequency and intensity of fires.

COMMUNITY HABITAT

10(a) Impact on composition of high value EVC? EVC= Plains Savannah (E); CMA=Mallee; Bioreg=Murray Mallee; Climate=VH. An infestation in Queensland has converted parts of the Mitchell grass downs into a thorny scrubland. “…a moderate canopy of prickly acacia reduces grass cover markedly” (Mackey 1998). Major displacement of some dominant species (grasses) within a strata (groundcover layer).

10(b) Impact on medium value EVC? EVC= grassy dry forest (D); CMA=Goulburn Broken; Bioreg=Central Victorian Uplantds; Climate=VH. An infestation in Queensland has converted parts of the Mitchell grass downs into a thorny scrubland. “…a moderate canopy of prickly acacia reduces grass cover markedly” (Mackey 1998). Major displacement of some dominant species (grasses) within a strata (groundcover layer).

10(c) Impact on low value EVC? EVC= Lowland Forest (LC); CMA=Goulburn Broken; Bioreg=Highlands-Northern Fall; Climate=VH. An infestation in Queensland has converted parts of the Mitchell grass downs into a thorny scrubland. “…a moderate canopy of prickly acacia reduces grass cover markedly” (Mackey 1998). Major displacement of some dominant species (grasses) within a strata (groundcover layer).

11. Impact on structure? An infestation in Queensland has converted parts of the Mitchell grass downs into a thorny scrubland. “…a moderate canopy of prickly acacia reduces grass cover markedly” (Mackey 1998). Serious impact on grasses.

12. Effect on threatened flora? The potential for A. nilotica ssp. indica to establish and naturalise in Victoria is highly unlikely due to ecoclimatic limitations (Thorp & Lynch 2000). No impact on threatened flora in Victoria.

FAUNA

13. Effect on threatened fauna? The potential for A. nilotica ssp. indica to establish and naturalise in Victoria is highly unlikely due to ecoclimatic limitations (Thorp & Lynch 2000). No impact on threatened fauna in Victoria.

14. Effect on non-threatened fauna? “Since even a moderate canopy cover of prickly acacia reduces grass cover markedly and changes the relative abundance of native plant species in favour of forbs and annual grasses, this, and the shift in structure toward a shrub community, is producing a dramatic effect on native fauna habitat and the overall ecology of the system” (Mackey 1998). Major impact on habitat.

15. Benefits fauna? “Its leaf is very digestible and has a high protein content” (Mackey 1998). May provide alternative food source for larger native herbivores.

16. Injurious to fauna? “Dogs cannot be used because of the many thorns on the ground” (Parsons & Cuthbertson 2001). Potential for injury to non-ungulate species.

PEST ANIMAL

17. Food source to pests? “…the Australian plague locust (Chortoicetes terminifera (Walker)) is reported to feed on it,” though without any known flow-on to impact on agricultural activities (Mackey 1998). Provides food for an environmental insect pest.

18. Provides harbor? Not known to provide harbor for pest species.

AGRICULTURE

19. Impact yield? “Dense infestations significantly reduce pasture production…and the access of stock to water. Under normal grazing pressure a 25–30% canopy cover of prickly acacia reduces pasture production by 50% compared with acacia-free pasture” (Mackey 1998). Significant reduction in carrying capacity leading to reduced yield.

20. Impact quality? Not known to affect the quality of produce

21. Affect land values? “Heavily infested land is almost worthless since reclamation costs are often close to, or exceed, the value of uninfested land” (Mackey 1998). Serious impact on land value.

22. Change land use? See comment in 21 above. Land may be abandoned for agricultural use.

23. Increase harvest costs? “Dense infestations of prickly acacia…increase mustering time and cost.” An increase in cost of more than 10 times the usual cost is reported (Mackey 1998). Increase in both time and labour to harvest produce.

24. Disease host/vector? “Prickly acacia is a host for a variety of organisms which attack it, but it does not appear to be a primary host for any other pests in Australia, though the Australian plague locust (Chortoicetes terminifera (Walker)) is reported to feed on it” (Mackey 1998).

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Assessment ratings originally made by the Victorian Department of Primary Industries.

The entry of this assessment was made possible through the generous support of The Weed's Network.

Attachments:

Present Distribution Acacia nilotica.doc
Potential Distribution Acacia nilotica.doc
distribution_map (4).png

referenced by (2)

wra1029: Common Name - P (via prickly acacia)wra1001: Common Name - G (via gum arabic tree)

Article: wra4903 (permalink)
Categories: :wra:a, :wra:inv1, :wra:invmh, :wra:inv2, :wra:invml, :wra:inv3, :wra:inv4, :wra:invl, :wra:inv5, :wra:inv6, :wra:inv7, :wra:invh, :wra:inv8, :wra:inv9, :wra:inv10, :wra:inv11, :wra:inv12, :wra:inv13, :wra:inv14, :wra:inv15, :wra:imp1, :wra:imph, :wra:imp2, :wra:imp3, :wra:imp4, :wra:impml, :wra:impl, :wra:imp5, :wra:imp6, :wra:imp7, :wra:impmh, :wra:imp8, :wra:imp9, :wra:imp10a, :wra:imp10b, :wra:imp10c, :wra:imp11, :wra:imp12, :wra:imp13, :wra:imp14, :wra:imp15, :wra:imp16, :wra:imp17, :wra:imp18, :wra:imp19, :wra:imp20, :wra:imp21, :wra:imp22, :wra:imp23, :wra:imp24
Date: 18 November 2009; 11:59:59 AM AEDT

Author Name: Niharika Anand
Author ID: anandn